Who do I get an iphone with more gigs without paying too much?

So I originally had an iPhone 5 64g. But it was stolen and long story short I now have an iphone 5 16g with no upgrades available until 4/2015. I miss being able to store all my music on my phone and really want to try to get a 64g again. I was wondering if this scheme I've devised would work… I already have a family talk plan with AT&T with one other line on it. Would it make any sense to add another line $399 for the new iphone plus $10/mo (plus the $20 data which i will later cancel). Switch out the sim cards when the new 64g iphone comes and sell the other 16g iphone 5 for almost $400. And then a.either get them to cancel the line b/c its "lost/stolen" or just b. Just keep paying $10/mo for 2 years b/c its cheaper then the cancel contract fee in the long run. Has anyone ever tried this/have a better suggestion.

In my opinion, I think it would but I'm not an AT&T rep. If its worth all the trouble than go for it!